DESCRIPTION (Applicant's Abstract): The respiratory epithelium is the first line of defense in the lung, and is constantly exposed to numerous airborne pathogens, allergens, and other noxious agents. Several innate host defenses have evolved to protect the lung, but a critical feature of pulmonary immunity is the ability of the airway to defend itself yet regulate the inflammatory response to avoid its injury and destruction. This inflammatory response is dysregulated in cystic fibrosis (CF), and similar defects may also exist in other airway diseases like asthma. Recent investigations suggest that an intrinsic, inhibitory mechanism is defective in chronic airway diseases and could account for exaggerated or persistent airway inflammation. Various effector cells that reside in the respiratory tract could be modulated by this inhibition, but we postulate that the respiratory epithelial cell is the primary target and is central to the airway's response to bacterial and antigenic stimuli. In this proposal, we will test this hypothesis by blocking the respiratory epithelium's response to such stimuli, using a novel delivery system that transports interleukin-10 (IL-10) to the epithelial lumen by exploiting the properties of the polymeric immunoglobulin receptor (pIgR). We have constructed fusion proteins that consist of single-chain Fv antibodies directed against the extracellular portion of plgR, or secretory component (SC), linked to the anti-inflammatory cytokine, human IL-10 (hIL-l0). Using this approach, we will be able to define the role(s) of the respiratory epithelial cell in the development of airway inflammation by concentrating the anti-inflammatory agent at the immediate epithelial surface. First, we will compare the penetration of free and "targeted" hIL-10 (i.e., anti-SC Fv/hIL-10 fusion protein) through epithelial monolayers in culture, and examine the immunomodulatory effects of these cytokines in model cell systems. We will then define the pharmacological and immunological properties of the targeted IL-10 in transgenic mice that express human pIgR in their airways, and establish that hIL-10 is effectively delivered to the respiratory epithelium. Finally, we will examine the effects of hIL-10 delivered specifically to the lumenal surface of the respiratory epithelium in disease models of endobronchial inflammation, and compare the anti-inflammatory effects of the fusion protein with free hIL-10. These investigations will allow us to define the mechanisms by which IL-l0 may act in the airway, and determine if such fusion proteins could potentially be used for therapeutic purposes in CF, asthma, and other airway diseases.